1. Field of the Invention
The present invention relates generally to a method and apparatus for calibrating detector cells and, more particularly, to a method and apparatus for storing and updating offsets for correction of a detected signal from photodetector cells.
2. Description of the Related Art
In a linear array of photodetector cells, each photodetector cell has a unique DC offset due to manufacturing differences, ageing and environmental factors such as temperature. Therefore, each photodetector cell must be individually calibrated to correct for the DC offset. Calibration of the photodetector cells must be quick and accurate when data from an antenna is being serially quantized from a linear array of a photodetector cells. Furthermore, the calibration must have an ability to accurately correct for only true DC offset errors by rejection of spurious noise and spikes which do not represent those factors such as manufacturing differences, ageing or steady state environmental conditions.
Previously, a one-time offset measurement of each photodetector cell in an array was made and the offset stored in a look-up table. A software correction was then performed on every pulse measurement. This approach slowed down an already overloaded processor and failed to provide for correction of photodetector cell DC offsets which change over time, such as instabilities due to temperature variations. Furthermore, the offset corrections using hardware addressed by cell number was very complicated.